The present invention relates to an imaging apparatus, and particularly to an imaging apparatus including both an optical zooming function and an electronic zooming function.
A zoom lens drive mechanism utilizing a stepping motor is already popular as a typical means for moving an optical zoom lens along an optical axis to effect zooming. In such a zoom lens drive mechanism, the zoom lens position is detected by forming an open loop with an optical zooming means, an optical zooming control means and a stepping motor and by continuously monitoring the number of driving steps of the stepping motor with the optical zooming control means in order to equivalently monitor the zoom lens position of the optical zooming means.
Moreover, in Japanese Patent Application Laid-Open No. HEI6-273658, it is indicated that an optical zooming means and an electronic zooming means can be smoothly interlocked for operation, on the occasion of transition to electronic zooming from optical zooming or transition to optical zooming from electronic zooming, by varying the magnifying power changing rate of the electronic zooming means and providing a parallel operating section, where the optical zooming means and electronic zooming means operate in parallel within a video camera in which there is provided both an optical zooming means and an electronic zooming means for purposes of extending the zooming range. In addition, it is also described in the same publication that the optical zooming means and electronic zooming means can be interlocked smoothly by changing the parallel operating sections for each zooming rate.
When a zoom lens is to be driven with a stepping motor via gears or the like, a mechanical play is inherently present at the engaging portions, etc. of the gears. In this case, when the amount of play is zero, the zoom lens position can be equivalently determined by monitoring the number of the drive steps of the stepping motor with an optical zooming control means.
However, if the amount of play increases, the error generated at the zooming position indicated by the optical zooming control means also increases. Moreover, when the driving direction is reversed, the lens drive first must be operated to take up the amount of play. The amount of play also fluctuates depending on the manufacturing process. Here, there is a problem in that, even if optical zooming control means are designed to the same specifications, the amount of play is not always equal and it also changes depending on temperature. This mechanical play also results in deviation of the parallel operating section for the optical zooming means and electronic zooming means from the optimum position during the interlocking operation of such optical and electronic zooming means. Under this condition, the optical zooming means and electronic zooming means can no longer be interlocked for proper operation even with the technique described in the Japanese Patent Application Laid-Open No. Hei 6-273658.